/Engine/Source/Runtime/Landscape/Public/LandscapeEdit.h
Updates weightmaps for all layers. Data points to packed data for all layers in the landscape info.
void SetAlphaData ( const [TSet](API\Runtime\Core\Containers\TSet)< [ULandscapeLayerInfoObject](API\Runtime\Landscape\ULandscapeLayerInfoObject) * > & DirtyLayerInfos, const int32 X1, const int32 Y1, const int32 X2, const int32 Y2, const uint8 * Data, int32 Stride, ELandscapeLayerPaintingRestriction PaintingRestriction )